1. Field of the Invention
The invention is related to a sliding bearing, e.g., a journal bearing having comprising at least two bearing elements, the bearing surfaces of which are slidably supported with respect to each other, at least one of the bearing surfaces being provided with a first type of cavities which may comprise a lubricating substance, and with a second type of cavities which may comprise a lubricating substance.
2. Description of the Related Art
Such a journal bearing is disclosed in US-A-2004/0228554. This document is related to a plain bearing which has a sliding member provided with a plurality of holes which become gradually larger as they get closer to both ends in axial direction from the centre side of the sliding member. In particular, the sliding member may be formed by the main bearing which rotatably supports a crankshaft. The purpose of this particular pattern of holes is to improve the conformability of the sliding surface in an early state of sliding. The process of forming the sliding surface in question is made necessary by the fact that the load acts predominantly on both end portions of the main bearing, as a result of which the bearing surface load may arise to an extremely high level in those end portions. Thereby, the lubricating oil film may be destroyed, leading to partial metallic contact and seizure.
With the aim of the mitigating this adverse effect, the total area of the openings of the recesses per unit area is made to become gradually larger closer to the ends of the bearing. Thereby, the pressurized area in the end portions decreases. Consequently, in those end portions the strength of the sliding member is reduced, whereby the sliding surface wears in conformity with the deflection of the mating member. Accordingly, the sliding surface is worn at an early stage in the useful life of the bearing. As a result of this wear, the types of cavities become to resemble each other whereby a quasi uniform behaviour is obtained over the width of the bearing.
Such a layout with, in the end, more or less uniform cavities is not fit for providing adequate lubrication both under circumstances wherein low friction and full lubricant film conditions prevail, as well as under conditions wherein poor lubrication conditions prevail. It appears that the requirements of low friction under full lubricant film conditions and improved poor lubrication behaviour are at variance with each other. This is clear from the fact that for efficient operation under full lubricant film conditions, very shallow cavities are required. Such very shallow cavities will promote the pressure build up in the lubricant under running conditions. On the other hand, for an acceptable poor lubrication behaviour, sufficient amounts of lubricant should be available within the cavities. Typically, the latter requirement would result in relatively deep cavities. As both these circumstances may occur in the same bearing, a compromise has to be struck so as to ensure the proper operation of the bearing under all circumstances.